The present invention relates to a novel curable composition which can be cured with moisture giving a rubbery substance having improved tensile properties and low residual tack and which has excellent storage stability. More particularly, the present invention relates to a curable composition comprising an organic polymer having a reactive silicon functional group in its molecule and a specific organic silicon compound, capable of giving a rubbery substance having improved tensile properties and low residul tack and having excellent storage stability.
As a polymer which is viscous liquid before curing and which can be cured even at room temperature to form a rubbery substance, there has been widely known a room temperature vulcanizable silicone rubber (hereinafter referred to as "RTV polysiloxane"). The RTV polysiloxane is suitable for use in sealants for building, molding materials, and the like. However, the RTV polysiloxane is expensive since its main chain is a polysiloxane, and is poor in some physical properties.
There has been proposed an elastomeric organic polymer curable at room temperature like the RTV polysiloxane whose main chain is not polysiloxane but an elastomeric organic polymer as shown in, for instance, U.S. Pat. No. 3,971,751. The elastomeric organic polymer has a reactive silicon functional group crosslikable by the formation of aa siloxane bond through a silanol condensation reaction and it is cured even at room temperature to form a rubbery substance, as shown in the following reaction scheme. ##STR1## Wherein X' is a hydrolyzable group. This elastomeric organic polymer is inexpensive compared to the RTV polysiloxane and has some characteristics which are not present in the polysiloxane.
Generally rubbers are required to have a low modulus of elasticity and high elongation as their tensile properties. On the other hand, important properties required for a room temperature curable polymer are to cure to the extent the surface of the cured product is not sticky (low residual tack) and to be stable during storage before curing (storage stability). In order to improve the modulus of elasticity or elongation of the cured product of the elastomeric organic polymer having the reactive silicon group, a method has been proposed using a composition comprising the elastomeric organic polymer and a monovalent compound or its derivative as shown in Japanese Unexamined Patent Publication No. 34066/1986 and No. 34067/1986.
This method is very simply and useful for controlling the tensile properties. However the composition disclosed in the above publications has a following drawback. That is, when the modulus of elasticity and elongation of cured product are sufficiently inproved, the residual tack of cured product or the storage stability of the composition deteriorates, and when the residual tack and the storage stability are sufficient, the improvement of the modulus of elasticity and elongation is insufficient.
An object of the present invention is to provide a curable composition comprising an elastomeric organic polymer having a reactive silicon functional group, which has improved modulus of elasticity and elongation of the cured product and low residual tack of the cured product, and excellent storage stability.
The above and other objects of the invention will become apparent from the description hereinafter.